The present invention relates to refiners for papermaking pulp or the like, and more particularly to improvements in refiners whose inlet admits stock for treatment by comminuting projections (e.g., ribs) on the neighboring surfaces of non-rotating refining members and rotary refining members.
The Pulp and Paper Industry uses pulp refiners to prepare papermaking fiber for production of paper products. The purpose of this refining process is to increase the strength potential of the pulp slurry before the pulp is formed into a sheet of paper. This is accomplished by passing the paper pulp between sets of refining members (also referred to as plates or discs) consisting of alternating bars and grooves that are in close proximity to each other. The gap between these plates is adjustable and can be as little as 2 thousandths of an inch. One of the plates rotates while the other plate in the set is stationary or non-rotating. The papermaking fiber is pumped through the refiner and passed between the refining members. The bar edges capture the papermaking fiber thus generating alternating compression and relaxation in the fiber.
The refining members are urged together by, for example, hydraulic piston and cylinder assemblies or by a motor that adjusts the position of one of the stationary plates. The close proximity of the rotating refining member to the non-rotating refining member under some circumstances can result in contact between the two plates. Also, since the plates are held apart only by the papermaking pulp passing between the plates, if the supply of pulp reduces or ceases, the plates can move into contact with each other. The plates coming together and making contact with each other is called “plate clashing”. This condition, if allowed to continue for sustained periods of time, results in rapid wear of the refining member bars and poor fiber development and paper strength properties. It is desirable to be able to recognize this condition when it occurs and make adjustments to the process, if possible, to eliminate it.
It is already known to utilize in a rotor refiner two coaxial plates, at least one of which is driven by a discrete prime mover and which have neighboring surfaces provided with ribs or otherwise configured projections which comminute the material to be treated while the material advances from the inlet toward the outlet of the stock chamber. It is also known to dispose two rotary discs between two stationary discs so that each rotary disc cooperates with a different stationary disc.
As discussed in Whyte U.S. Pat. No. 4,627,578, there have been attempts to detect plate clashing using the techniques of measuring increased work, increased energy requirements, or bearing vibration resonances during clashing, and then backing off the plates. Whyte U.S. Pat. No. 4,627,578 disclosed an apparatus for controlling the relative position of refining members including vibration sensing means, such as a transducer fixed for example to one of the stationary plates. The transducer is preferably an accelerometer. According to this patent, the transducer is used to detect vibrations caused by passage of material between the refining members by detecting any decrease in vibrations from normal or safe operating conditions due to a reduced quantity of material passing between the refining members. A control means increases the distance between the refining members, when the decreased vibrations are sensed, in order to prevent clashing of the refining members.